Reverse-jet swirl pulverized coal burner with multi-stage recirculations

ABSTRACT

A reverse-jet swirl pulverized coal burner with multi-stage recirculations includes a pre-combustion housing, a primary coal-air structure, a rich-lean output structure, an inner secondary air structure, and an outer secondary air structure. The pre-combustion housing has a pre-combustion chamber and a housing outlet. The primary coal-air structure is configured to separate a primary coal-air flow into a fuel-rich coal-air flow and a fuel-lean coal-air flow. The rich-lean output structure is configured to output the fuel-lean coal-air flow and block the fuel-rich coal-air flow to make the fuel-rich coal-air flow reversely flow to the pre-combustion chamber. The inner secondary air structure is configured to introduce an inner secondary air into the pre-combustion chamber, thereby forming a first-stage recirculation zone in the pre-combustion chamber and forming a second-stage recirculation zone. The outer secondary air structure is configured to form a third-stage recirculation zone at the housing outlet.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority of China Patent Application No.201910283921.6, filed on Apr. 10, 2019, entitled “REVERSE-JET SWIRLPULVERIZED COAL BURNER WITH MULTI-STAGE RECIRCULATIONS”, the content ofwhich is hereby incorporated by reference in its entirety. The presentapplication is a continuation under 35 U.S.C. § 120 of internationalpatent application PCT/CN2020/082896, filed on Apr. 2, 2020, entitled“REVERSE-JET SWIRL PULVERIZED COAL BURNER WITH MULTI-STAGERECIRCULATIONS”, the content of which is also hereby incorporated byreference in its entirety.

TECHNICAL FIELD

The present application relates to the technical field of pulverizedcoal combustion equipment, and particularly relates to a reverse-jetswirl pulverized coal burner with multi-stage recirculations.

BACKGROUND

In China, coal-fired industrial boilers are the main coal combustionequipment other than power plant boilers. Conventional coal-firedindustrial boilers are mainly laminar combustion grate boilers and chaingrate boilers. Lump coal is placed on a stationary or traveling grate toform a fuel layer. Air is introduced from the bottom of the grate, andflows through the fuel layer for combustion reaction. Limited bycombustion space and effective reaction area, this type of boilergenerally has a problem of low thermal efficiency.

In recent years, with the continuous development of pulverized coalprocessing, transportation, storage, and combustion technologies,chamber combustion of pulverized coal has gradually replaced coallaminar combustion, and has been widely used in coal-fired boilers. Thisapproach adopts air-carrying pulverized coal particles, which aresprayed into the furnace for suspension combustion, thereby enhancingmixing and contact between gas and solid and improving combustionefficiency and thermal efficiency of the boiler. However, in actualoperation, compared with power plant boilers, industrial boilers haveoperating characteristics that characteristics of pulverized coal aregreat differentiated and boiler loads are widely varied. Whereas, mostof present design guidelines for industrial pulverized coal boilers arebased on specific selected coal types and a full-load operatingcondition, resulting in many problems such as poor combustion stability,great mechanical loss in incomplete combustion, and large NO_(x)emissions when other coal types are used or mixed or the boiler isoperated at a low load.

With the gradually increased attention of the country to environmentalprotection issues, the existing pulverized coal combustion technology ofindustrial boilers is difficult to meet the increasingly strictpollutant emission standards. The development of pulverized coalcombustion equipment with high efficiency, low NO_(x) generation, strongcoal-type adaptability, and strong combustion stability at a low loadfor industrial pulverized coal boilers has become an urgent need in theindustry.

SUMMARY

In view of this, there is a need to provide a reverse-jet swirlpulverized coal burner with multi-stage recirculations.

A reverse-jet swirl pulverized coal burner with multi-stagerecirculations includes:

-   -   a pre-combustion housing, the pre-combustion housing having a        pre-combustion chamber and a housing outlet located on one side        of the pre-combustion chamber;    -   a primary coal-air structure passing through the pre-combustion        housing and extending into the pre-combustion chamber, the        primary coal-air structure being configured to separate a        primary coal-air flow into a fuel-rich coal-air flow and a        fuel-lean coal-air flow, and an outlet end of the primary        coal-air structure extending toward the housing outlet;    -   a rich-lean output structure disposed at the outlet end of the        primary coal-air structure, the rich-lean output structure being        configured to output the fuel-lean coal-air flow and block the        fuel-rich coal-air flow to make the fuel-rich coal-air flow        reversely flow to the pre-combustion chamber;    -   an inner secondary air structure disposed on the pre-combustion        housing and around the primary coal-air structure, the inner        secondary air structure is configured to introduce an inner        secondary air into the pre-combustion chamber, thereby forming a        first-stage recirculation zone in the pre-combustion chamber and        forming a second-stage recirculation zone at an end of the        rich-lean output structure away from the primary coal-air        structure; and    -   an outer secondary air structure sleeved outside the        pre-combustion housing, the outer secondary air structure being        configured to transport an outer secondary air, thereby forming        a third-stage recirculation zone at the housing outlet.

In an embodiment, the pre-combustion housing includes a cone section andan expansion section connected to the cone section. An end of theexpansion section away from the cone section is the housing outlet ofthe pre-combustion housing. An inclination angle of the expansionsection is greater than an inclination angle of the cone section.

In an embodiment, the inclination angle a of the cone section satisfies0°<α≤20°, and the inclination angle β of the expansion section is in arange from 20° to 50°.

In an embodiment, the primary coal-air structure includes a primarycoal-air flow pipe, a fixing axle, and a plurality of swirl vanes. Thefixing axle is located adjacent to an outlet end of the primary coal-airflow pipe. The plurality of swirl vanes are connected to an inner wallof the primary coal-air flow pipe and the fixing axle, and areconfigured to separate the primary coal-air flow into the fuel-richcoal-air flow and the fuel-lean coal-air flow.

In an embodiment, the rich-lean output structure includes arecirculation baffle and a fuel-lean coal-air flow pipe penetratingthrough the recirculation baffle. The recirculation baffle is located atthe outlet end of the primary coal-air flow pipe. A surface of therecirculation baffle facing the primary coal-air flow pipe has arecirculation slot. The recirculation slot is configured to guide thefuel-rich coal-air flow to flow reversely to the pre-combustion chamber.A shape of an inner wall of the recirculation slot is straight orcurved. A fuel-rich coal-air flow channel with a circular cross-sectionis formed between the inner wall of the recirculation slot and an outerwall of the primary coal-air flow pipe to reverse the fuel-rich coal-airflow. The fuel-lean coal-air flow pipe, having one end extending into acentral area of the outlet end of the primary coal-air flow pipe, isconfigured to output the fuel-lean coal-air flow coming from the primarycoal-air flow pipe.

In an embodiment, the recirculation baffle has a conical shape, and across-sectional size of an end of the recirculation baffle toward theprimary coal-air flow pipe is smaller than a cross-sectional size ofanother end of the recirculation baffle away from the primary coal-airflow pipe. The rich-lean output structure includes a fixing rib thatconnects the recirculation baffle to the primary coal-air flow pipe.

In an embodiment, the inner secondary air structure includes astrong-swirl inner secondary air assembly, a weak-swirl inner secondaryair assembly, and a direct-flow inner secondary air channel. Thestrong-swirl inner secondary air assembly is sleeved outside the primarycoal-air structure. The weak-swirl inner secondary air assembly issleeved outside the strong-swirl inner secondary air assembly. Thedirect-flow inner secondary air channel is sleeved outside theweak-swirl inner secondary air assembly. Tangential swirling speeds ofthe secondary air respectively conveyed by the strong-swirl innersecondary air assembly, the weak-swirl inner secondary air assembly, andthe direct-flow inner secondary air channel gradually decrease.

In an embodiment, the strong-swirl inner secondary air assembly includesa strong-swirl inner secondary air channel and strong-swirl axial vanesdisposed in the strong-swirl inner secondary air channel. Thestrong-swirl axial vanes are configured to make the inner secondary airin the strong-swirl inner secondary air channel have a tangentialswirling speed.

In an embodiment, an outlet angle θ of the strong-swirl axial vanesranges from 50° to 80°.

In an embodiment, the weak-swirl inner secondary air assembly includes aweak-swirl inner secondary air channel and weak-swirl axial vanesdisposed in the weak-swirl inner secondary air channel. The weak-swirlaxial vanes are configured to make the inner secondary air in theweak-swirl inner secondary air channel have a tangential swirling speed.

In an embodiment, an outlet angle δ of the weak-swirl axial vanes rangesfrom 20° to 50°.

In an embodiment, the reverse-jet swirl pulverized coal burner furtherincludes an annular connector. The annular connector is located betweenthe strong-swirl inner secondary air assembly and the primary coal-airstructure, and connects and fixes the strong-swirl inner secondary airassembly to the primary coal-air structure.

In an embodiment, the outer secondary air structure includes an outersecondary air inlet channel, an outer secondary air outlet channel, andtangential vanes. The outer secondary air inlet channel and the outersecondary air outlet channel are connected and fluid communicated in astepped manner. The tangential vanes are disposed in a connection areabetween the outer secondary air inlet channel and the outer secondaryair outlet channel.

In an embodiment, an outlet angle y of the tangential vane ranges from15° to 40°.

In an embodiment, the outer secondary air structure further includes aseparation annulus. The separation annulus is disposed at an end of theouter secondary air outlet channel, and located on the outer wall of theexpansion section.

By adopting the above technical solutions, the present application hasat least the following technical effects:

In the reverse jet swirl pulverized coal burner with multi-stagerecirculations of the present application, the primary coal-airstructure separates the primary coal-air flow into the fuel-richcoal-air flow and the fuel-lean coal-air flow. After being blocked bythe rich-lean output structure, the fuel-rich coal-air flow reverselyflows to the pre-combustion chamber, and cooperates with the innersecondary air to form the first-stage recirculation zone in thepre-combustion chamber. The fuel-rich coal-air flow is entrained intothe first-stage recirculation zone, burns, and releases heat. Meanwhile,as the recirculation baffle has a conical shape, a second-stagerecirculation zone is formed at the side of the rich-lean outputstructure away from the primary coal-air structure, in which thefuel-lean coal-air flow is heated and ignited. After that, the airflowsand unburned coal particles in the pre-combustion chamber are ejectedout from the housing outlet of the pre-combustion housing. The outersecondary air structure forms the outer secondary air into a third-stagerecirculation zone at the housing outlet, which further promotes burnoutand stable combustion of the unburned pulverized coal, which is finallysprayed into a furnace. As such, the primary coal-air flow isconcentrated and separated, and then undergone combustion in threestages of recirculation zones, which is beneficial to ignition, stablecombustion, and burnout of pulverized coal under different coal typesand boiler load conditions while reducing NO_(x) production during thepulverized coal combustion. The problems of insufficient pulverized coalburnout, poor combustion stability at a low load, and high NO_(x)emission in current industrial pulverized coal boilers are effectivelysolved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front cross-sectional view of a reverse-jet swirl pulverizedcoal burner with multi-stage recirculations according to an embodimentof the present application.

FIG. 2 is a side view of the reverse-jet swirl pulverized coal burnerwith multi-stage recirculations shown in FIG. 1.

FIG. 3 is a cross-sectional view along A-A of the reverse-jet swirlpulverized coal burner with multi-stage recirculations shown in FIG. 2.

FIG. 4 is a perspective view of a strong-swirl inner secondary airassembly in the reverse-jet swirl pulverized coal burner withmulti-stage recirculations shown in FIG. 1.

FIG. 5 is a perspective view of a weak-swirl inner secondary airassembly in the reverse-jet swirl pulverized coal burner withmulti-stage recirculations shown in FIG. 1.

FIG. 6 is a cross-sectional view along B-B of the reverse-jet swirlpulverized coal burner with multi-stage recirculations shown in FIG. 2.

FIG. 7 is a perspective view of tangential vanes installed on apre-combustion housing of the reverse-jet swirl pulverized coal burnerwith multi-stage recirculations shown in FIG. 1.

FIG. 8 is a perspective view of swirl vanes of a primary coal-airstructure in the reverse-jet swirl pulverized coal burner withmulti-stage recirculations shown in FIG. 1.

FIG. 9 is a principle view of the reverse jet swirl pulverized coalburner with multi-stage recirculations shown in FIG. 1.

Wherein:

100-reverse-jet swirl pulverized coal burner with multi-stagerecirculations; 110-pre-combustion housing; 111-pre-combustion chamber;112-cone section;

113-expansion section; 120-primary coal-air structure; 121-primarycoal-air flow pipe; 122-fixing axle; 123-swirl vane; 130-rich-leanoutput structure; 131-recirculation baffle; 1311-recirculation slot;132-fuel-lean coal-air flow pipe; 133-fuel-rich coal-air flow channel;134-fixing rib; 140-inner secondary air structure; 141-strong-swirlinner secondary air assembly; 1411-strong-swirl inner secondary airchannel; 1412-strong-swirl axial vane; 142-weak-swirl inner secondaryair assembly; 1421-weak-swirl inner secondary air channel;1422-weak-swirl axial vane; 143-direct-flow inner secondary air channel;1431-supporting rib; 150-outer secondary air structure; 151-outersecondary air inlet channel; 152-outer secondary air outlet channel;153-tangential vane; 154-separation annulus; 160-annular connector.

DETAILED DESCRIPTION

The reverse-jet swirl pulverized coal burner with multi-stagerecirculations of the present application will now be described indetail with reference to the accompanying drawings and embodiments inorder to make the objects, technical solutions, and advantages of thepresent application more clear. It should be understood that thespecific embodiments described herein are only for explaining thepresent application, and not intended to limit the present application.

The serial numbers assigned to the components herein, such as “first”,“second”, etc., are merely used to distinguish the described objects anddo not have any sequence or technical meaning. The meanings of“connection” and “joining” mentioned in the present application includedirect and indirect connection (joining) unless otherwise specified. Inthe description of the present application, it should be understood thatthe terms “upper”, “lower”, “front”, “rear”, “left”, “right”,“vertical”, “horizontal”, “top”, “bottom”, “inner”, “outer”,“clockwise”, “counterclockwise”, etc. indicate the orientations orpositional relationships on the basis of the drawings. These terms areonly for describing the present invention and simplifying thedescription, rather than indicating or implying that the related devicesor elements must have the specific orientations, or be constructed oroperated in the specific orientations, and therefore cannot beunderstood as limitations of the present application.

In the present application, unless expressly stipulated and definedotherwise, a first feature, when referred to as being located “on” or“under” a second feature, may be in direct contact with the secondfeature, or in indirect contact with the second feature via anintermediate element. Moreover, a first feature, when referred to asbeing located “on”, “above”, “over” a second feature, may be locatedright above or obliquely above the second feature, or merely located ata horizontal level higher than the second feature; a first feature, whenreferred to as being located “under”, “below”, “beneath” a secondfeature, may be located right below or obliquely below the secondfeature, or merely located at a horizontal level lower than the secondfeature.

Referring to FIG. 1 to FIG. 9, the present application provides areverse-jet swirl pulverized coal burner 100 with multi-stagerecirculations. The reverse-jet swirl pulverized coal burner 100 can beapplied in an industrial pulverized coal boiler. The reverse-jet swirlpulverized coal burner 100 of the present application can realize theseparation between rich and lean pulverized coal, multi-stagerecirculations of air flow, and air-staged combustion, which isbeneficial to ignition, stable combustion, and burnout of pulverizedcoal under the conditions of different coal types and different boilerloads, and can reduce NO_(x) generation during combustion of pulverizedcoal.

In an embodiment, the reverse jet swirl pulverized coal burner 100includes a pre-combustion housing 110, a primary coal-air structure 120,a rich-lean output structure 130, an inner secondary air structure 140,and an outer secondary air structure 150. The primary coal-air structure120 partially extends into the pre-combustion housing 110, and is fluidcommunicated with the pre-combustion housing 110. The rich-lean outputstructure 130 is located at the end of the primary coal-air structure120 in the pre-combustion housing 110. The inner secondary air structure140 is sleeved outside the primary coal-air structure 120 and is locatedat an end of the pre-combustion housing 110, and the inner secondary airstructure 140 is fluid communicated with the pre-combustion housing 110.The outer secondary air structure 150 is sleeved outside thepre-combustion housing 110.

Specifically, the pre-combustion housing 110 has a pre-combustionchamber 111 and a housing outlet located at one side of thepre-combustion chamber 111. The primary coal-air structure 120 passesthrough the pre-combustion housing 110 and extends into thepre-combustion chamber 111 to separate a primary coal-air flow into afuel-rich coal-air flow and a fuel-lean coal-air flow. An outlet end ofthe primary coal-air structure 120 extends toward the housing outlet.The rich-lean output structure 130 is disposed at an outlet end of theprimary coal-air structure 120. The rich-lean output structure 130 isconfigured to output the fuel-lean coal-air flow and block the fuel-richcoal-air flow to make the fuel-rich coal-air flow reversely flow to thepre-combustion chamber 111. The inner secondary air structure 140 isdisposed on the pre-combustion housing 110 and around the primarycoal-air structure 120. The inner secondary air structure 140 isconfigured to introduce an inner secondary air into the pre-combustionchamber 111, thereby forming a first-stage recirculation zone F in thepre-combustion chamber 111 and forming a second-stage recirculation zoneM at an end of the rich-lean output structure 130 away from the primarycoal-air structure 120. The outer secondary air structure 150 is sleevedoutside the pre-combustion housing 110, and is configured to transportan outer secondary air, thereby forming a third-stage recirculation zoneN at the housing outlet.

The primary coal-air structure 120 introduces the primary coal-air flowinto the pre-combustion chamber 111 of the pre-combustion housing 110.During the introducing of the primary coal-air flow, the primarycoal-air structure 120 separates the primary coal-air flow to form thefuel-rich coal-air flow and the fuel-lean coal-air flow. When flowingfrom the primary coal-air structure 120 to the pre-combustion chamber111, the separated fuel-rich coal-air flow and fuel-lean coal-air flowis guided into the pre-combustion chamber 111 in different directions bythe rich-lean output structure 130. The fuel-rich coal-air flow enteredthe rich-lean output structure 130 is blocked by the rich-lean outputstructure 130, causing the fuel-rich coal-air flow to flow in a reverseddirection. That is to say, the fuel-rich coal-air flow in thepre-combustion chamber 111 flows in the direction opposite to a flowingdirection. The flowing direction refers to the direction of the primarycoal-air flow entering the pre-combustion chamber 111. The fuel-leancoal-air flow continues to flow in the flow direction after passingthrough the rich-lean output structure 130.

At the same time, the inner secondary air flows into the pre-combustionchamber 111 through the inner secondary air structure 140 and surroundsthe primary coal-air structure 120. The inner secondary air, during theflowing, interacts with the fuel-rich coal-air flow which flows in thereversed direction to form the first-stage recirculation zone F in thecombustion chamber 111. Because the reversely flowing fuel-rich coal-airflow can be easily entrained into the first-stage recirculation zone F,the fuel-rich coal-air flow whirls, burns, and releases heat in thefirst-stage recirculation zone F to generate a high-temperature flow,which then passes by the rich-lean output structure 130 and ejects outfrom the housing outlet of the pre-combustion housing 110. In addition,when passing by the rich-lean output structure 130, the high-temperatureflow forms the second-stage recirculation zone M at the side of therich-lean output structure 130 away from the primary coal-air structure120. A reunion between this portion of reversely flowinghigh-temperature flow and the fuel-lean coal-air flow ejected out fromthe rich-lean output structure 130 promotes elevating temperature of thefuel-lean coal-air flow, and thus heats and ignites the fuel-leancoal-air flow.

Then, the airflows and unburned coal particles in the pre-combustionchamber 111 are ejected out from the housing outlet of thepre-combustion housing 110. At this time, the outer secondary air isoutput from the outer secondary air structure 150 to the outside of thepre-combustion housing 110, thereby forming a third-stage recirculationzone N at the housing outlet of the pre-combustion housing 110, and thusalso generating a high-temperature recirculation fluid at the outlet ofthe reverse-jet swirl pulverized coal burner 100 with multi-stagerecirculations, which further promotes burnout and stable combustion ofthe unburned coal particles ejected from the pre-combustion chamber 111.In addition, the amount of oxygen required at the initial stage ofpulverized coal combustion is respectively supplied in two stages byinner secondary air structure 140 and outer secondary air structure 150,so that pulverized coal is always burned in a reducing atmosphere,thereby reducing NO_(x) generation during the combustion of pulverizedcoal.

In this way, after the primary coal-air flow is concentrated andseparated, it is burned in three stages of recirculation zone, which isconducive to the ignition, stable combustion, and burnout of pulverizedcoal with different coal types and under different load conditions, andis conducive to reduce NO_(x) generation in the pulverized coalcombustion process, thereby effectively solving the problems ofinsufficient pulverized coal burnout, poor combustion stability at a lowload, and high NO_(x) emissions in a current industrial pulverized coalboiler.

In an embodiment, the pre-combustion housing 110 includes a cone section112. The cross-sectional size of the cone section 112 graduallyincreases along the flow direction of the primary coal-air flow in theprimary coal-air structure 120. In this way, as the swirling innersecondary air adjacent to the primary coal-air structure 120 driving theprimary coal-air flow to flow, a low pressure zone is formed in thecentral area of the swirling air flow. In addition, the side wall of thecone section 112 of the pre-combustion housing 110 has an inclinationangle. During the flowing of the inner secondary air from top to bottomin the pre-combustion housing 110, the flow area of the air flowgradually expands, so that the flow rate of the air flow decreases, andthe static pressure gradually increases. The above two reasons worktogether to make part of the inner secondary air flow reversely to thelow pressure zone during the flowing of the inner secondary air in thepre-combustion chamber 111, thus forming the first-stage recirculationzone F in the pre-combustion chamber 111.

In an embodiment, the pre-combustion housing 110 further includes anexpansion section 113 connected to the cone section 112. An end of theexpansion section 113 away from the cone section 112 is the housingoutlet of the pre-combustion housing 110. The cross-sectional size ofthe expansion section 113 gradually increases along the flow directionof the primary coal-air flow in the primary coal-air structure 120.

In an embodiment, the inclination angle of the expansion section 113 isgreater than the inclination angle of the cone section 112. In a furtherembodiment, the range of the inclination angle a of the cone section 112is 0°<α≤20°. The inclination angle β of the expansion section 113 is ina range from 20° to 50°.

In an embodiment, the primary coal-air structure 120 includes a primarycoal-air flow pipe 121, a fixing axle 122, and a plurality of swirlvanes 123. The fixing axle 122 is located adjacent to an outlet end ofthe primary coal-air flow pipe 121. The plurality of swirl vanes 123 areconnected to the inner wall of the primary coal-air flow pipe 121 andthe fixing axle 122, and are configured to separate the primary coal-airflow into the fuel-rich coal-air flow and the fuel-lean coal-air flow.The fixing axle 122 is configured to fix the swirl vanes 123. The swirlvanes 123 can make the primary coal-air flow passed therethrough flowswirly.

The primary coal-air flow is introduced from the end of the primarycoal-air flow pipe 121 outside the pre-combustion housing 110, and flowsinitially in a straight line after entering the primary coal-air flowpipe 121. Under the action of the swirl vanes 123, the primary coal-airflow passing the swirl vanes 123 is transformed from a straight lineflow (i.e., a direct flow) to a high-speed swirling flow. During thehigh-speed swirling of the primary coal-air flow, the coal particles,due to the high density thereof, are subjected to a large centrifugalforce and thrown to the region adjacent to the inner wall of the primarycoal-air flow pipe 121, so that the pulverized coal in the regionadjacent to the inner wall of the primary coal-air flow pipe 121 has ahigher concentration, and the pulverized coal in the central area of theprimary coal-air flow pipe 121 has a lower concentration. The pulverizedcoal air flow further flows in the primary coal-air flow pipe 121, andis output and formed the fuel-rich coal-air flow and the fuel-leancoal-air flow through the rich-lean output structure 130. The fuel-richcoal-air flow flows in the reversed direction to the pre-combustionchamber 111. The fuel-lean coal-air flow flows into the pre-combustionchamber 111 in a straight line through a fuel-lean coal-air flow pipe132 in the rich-lean output structure 130.

It can be understood that the primary coal-air flow can be concentratedby passing through the swirl vanes 123, so that the pulverized coalconcentration in the fuel-rich coal-air flow increases to more than twotimes of that before the concentration, which is beneficial to reduceheat of ignition to combustion required by different coal types. Thispart of pulverized coal, i.e., the pulverized coal in the fuel-richcoal-air flow, is burnt in advance to form the main flame, which heatsand ignites the fuel-lean coal-air flow and other unburned pulverizedcoal particles. Moreover, by concentrating the primary coal-air flow,the staged combustion of the rich and lean pulverized coals can beeffectively realized, which is conducive to form a strong reduction zonein the pulverized coal combustion flame, so that the N element releasedduring the pulverized coal combustion is mainly transformed into NH₃ orN₂, inhibiting NO_(x) production.

In an embodiment, the rich-lean output structure 130 includes arecirculation baffle 131 and a fuel-lean coal-air flow pipe 132penetrating through the recirculation baffle 131. The recirculationbaffle 131 is located at the outlet end of the primary coal-air flowpipe 121. The surface of the recirculation baffle 131 facing the primarycoal-air flow pipe 121 has a recirculation slot 1311. The recirculationslot 1311 is configured to guide the fuel-rich coal-air flow to flowreversely to the pre-combustion chamber 111. The shape of the inner wallof the recirculation slot 1311 is straight and/or curved. A fuel-richcoal-air flow channel 133 with a circular cross-section is formedbetween the inner wall of the recirculation slot 1311 and the outer wallof the primary coal-air flow pipe for the reverse flowing of thefuel-rich coal-air flow. The fuel-lean coal-air flow pipe 132, havingone end extending into the central area of the outlet end of the primarycoal-air flow pipe 121, is configured to output the fuel-lean coal-aircoming flow from the primary coal-air flow pipe 121.

With the further flowing of the pulverized coal air flow, when thepulverized coal air flow reaches the outlet end of the primary coal-airflow pipe 121, the air flow with the lower pulverized coal concentrationin the central area directly faces the fuel-lean coal-air flow pipe 132,so that this part of the pulverized coal air flow is straightly ejectedfrom the fuel-lean coal-air flow pipe 132 to form the fuel-lean coal-airflow. At the same time, the air flow with the higher pulverized coalconcentration adjacent to the inner wall of the primary coal-air flowpipe 121 directly faces the recirculation slot 1311 of the recirculationbaffle 131. Since the fuel-rich coal-air flow channel 133 in a circularshape is formed by the inner wall of the recirculation slot 1311 and theouter wall of the primary coal-air flow pipe 121, the high-concentrationpulverized coal air flow will enter the fuel-rich coal-air flow channel133. Guided by the inner wall of the recirculation slot 1311, thehigh-concentration pulverized coal air flow is sprayed into thepre-combustion chamber 111 in the reversed direction along the outerwall of the primary coal-air flow pipe 121, thereby forming thereversely ejected fuel-rich coal-air flow.

It can be understood that the primary coal-air flow pipe 121 and thefirst-stage recirculation zone F are adjacent to each other. In thisway, the fuel-rich coal-air flow can flow next to the first-stagerecirculation zone F, directly affected by the heat radiation of thehigh-temperature first-stage recirculation zone F, which is conducive tothe temperature increasing and ignition of the fuel-rich coal-air flow.Since the fuel-rich coal-air flow is sprayed into the pre-combustionchamber 111 near the first-stage recirculation zone F, it is easier forthe fuel-rich coal-air flow to be entrained into the first-stagerecirculation zone F during the flowing. The rich coal-air flow swirlsand burns in the first-stage recirculation zone F to release heat, thenpasses by the recirculation baffle 131, and is ejected out from thepre-combustion chamber 111. In addition, the primary coal-air flow flowsin the primary coal-air flow pipe 121 and enters the pre-combustionchamber 111 through the recirculation baffle 131. When entering thepre-combustion chamber 111, the primary coal-air flow can cool theprimary coal-air flow pipe 121 and the recirculation baffle 131 torealize a function of cooling protection.

Exemplarily, the bottom of the recirculation slot 1311 has an arc shape,and the side wall of the recirculation slot 1311 has a straight shape.In this way, an annular fuel-rich coal-air flow channel 133 with aU-shaped cross-section is formed between the inner wall of therecirculation slot 1311 and the outer wall of the primary coal-air flowpipe 121 to facilitate the reversely flowing of the pulverized coal airflow. The fuel-lean coal-air flow pipe 132 has a fuel-lean coal-air flowchannel with a straight cylindrical shape.

Optionally, the primary coal-air flow pipe 121 and the recirculationbaffle 131 are located on the central axis of the pre-combustion chamber111. The fixing axle 122 is located on a central axis of the primarycoal-air flow pipe 121.

In an embodiment, the recirculation baffle 131 has a conical shape, andthe cross-sectional size of the end of the recirculation baffle 131toward the primary coal-air flow pipe 121 is smaller than thecross-sectional size of the end of the recirculation baffle 131 awayfrom the primary coal-air flow pipe 121. By adopting the conicalrecirculation baffle 131, a low pressure area can be formed at the sideof the recirculation baffle 131 away from the primary coal-air flow pipe121. In this way, when the high-temperature fluid generated in thecombustion in the first-stage recirculation zone F passes by the conicalrecirculation baffle 131, a low-pressure zone can be formed behind therecirculation baffle 131, so that part of the high-temperature fluidwill recirculate behind the recirculation baffle 131 to form asecond-stage recirculation zone M. This part of the recirculatedhigh-temperature fluid meets the fuel-lean coal-air flow ejected fromthe fuel-lean coal-air flow pipe 132 in the recirculation baffle 131,which will promote the temperature increasing of the fuel-lean coal-airflow, heating and igniting the fuel-lean coal-air flow. Then, the airflows and unburned pulverized coal particles in the pre-combustionchamber 111 are ejected out from the pre-combustion chamber 111.

In an embodiment, the rich-lean output structure 130 includes a fixingrib 134. The fixing rib 134 connects the recirculation baffle 131 andthe primary coal-air flow pipe 121, which can ensure that therecirculation baffle 131 is reliably fixed to the outlet end of theprimary coal-air flow pipe 121.

It can be understood that after the rich-lean separation of the primarycoal-air flow by the primary coal-air structure 120, the weight of thecoal particles contained in the fuel-lean coal-air flow accounts for10%-20% of the total weight of pulverized coal, and the air volume ofthe fuel-lean coal-air flow accounts for 60% to 70% of the total airvolume of the primary coal-air flow; the weight of the coal particlescontained in the fuel-rich coal-air flow accounts for 80% to 90% of thetotal weight of pulverized coal, and the air volume of the fuel-richcoal-air flow accounts for 30%-40% of the total air volume of theprimary coal-air flow. Due to the high concentration of pulverized coalin fuel-rich coal-air flow, the ignition heat of the fuel-rich coal-airflow is reduced, which is conducive to the ignition of the fuel-richcoal-air flow, and enhances combustion stability at a low load and coaltype adaptability. Moreover, the pulverized coal flow burns under thefuel-rich condition, which is beneficial to reduce the generation ofNO_(x).

In an embodiment, the inner secondary air structure 140 includes astrong-swirl inner secondary air assembly 141, a weak-swirl innersecondary air assembly 142, and a direct-flow inner secondary airchannel 143. The strong-swirl inner secondary air assembly 141 issleeved outside the portion of the primary coal-air structure 120outside the pre-combustion housing 110. The weak-swirl inner secondaryair assembly 142 is sleeved outside the strong-swirl inner secondary airassembly 141. The direct-flow inner secondary air channel 143 is sleevedoutside the weak-swirl inner secondary air assembly 142. The tangentialswirling speeds of the secondary air respectively conveyed by thestrong-swirl inner secondary air assembly 141, the weak-swirl innersecondary air assembly 142, and the direct-flow inner secondary airchannel 143 gradually decrease. That is, the primary coal-air structure120, the strong-swirl inner secondary air assembly 141, the weak-swirlinner secondary air assembly 142, and the direct-flow inner secondaryair channel 143 are orderly arranged from the inside to the outside, andthe strong-swirl inner secondary air assembly 141, the weak-swirl innersecondary air assembly 142 and the direct-flow inner secondary airchannel 143 are arranged next to each other from the inside to theoutside.

In other words, the inner secondary air is divided into three layers.The swirling strength of the inner secondary air conveyed by thestrong-swirl inner secondary air assembly 141 is greater than theswirling strength of the inner secondary air conveyed by the weak-swirlinner secondary air assembly 142. The direct-flow inner secondary airchannel 143 conveys the direct-flow inner secondary air. In this way,the inner secondary air conveyed by the strong-swirl inner secondary airassembly 141 has a larger tangential swirling speed when being sprayedinto the pre-combustion chamber 111, the inner secondary air conveyed bythe weak-swirl inner secondary air assembly 142 has a smaller tangentialswirling speed when being sprayed into the pre-combustion chamber 111,and the inner secondary air conveyed by the direct-flow inner secondaryair channel 143 has no tangential swirling speed and is sprayed into thepre-combustion chamber 111 as a direct flow. In other words, thestrong-swirl inner secondary air assembly 141 conveys the strongswirling inner secondary air, the weak-swirl inner secondary airassembly 142 conveys the weak swirling inner secondary air, and thedirect-flow inner secondary air channel 143 conveys the direct-flowinner secondary air.

After the overall inner secondary air is sprayed into the pre-combustionchamber 111 as above, a speed distribution is formed such that theswirling strength of the inner secondary air is gradually reduced tozero from the inner side to the outer side in the pre-combustion chamber111. Since the inner secondary air adjacent to the primary coal-air flowpipe 121 has a relatively large swirling tangential speed, during thehigh-speed swirling of the air flow, a low pressure zone is formed inthe central area of the swirling flow. In addition, since the conesection 112 has an inclination angle, during the flowing of the innersecondary air from top to bottom in the pre-combustion chamber 111, theflow area of the air flow gradually expands, so that the flow rate ofthe air flow decreases, and the static pressure gradually increases. Theabove two reasons work together to make part of the inner secondary airflow reversely to the low pressure zone during the flowing of the innersecondary air in the pre-combustion chamber 111, thus forming thefirst-stage recirculation zone F.

In an embodiment, the strong-swirl inner secondary air assembly 141includes a strong-swirl inner secondary air channel 1411 andstrong-swirl axial vanes 1412 disposed in the strong-swirl innersecondary air channel 1411. The strong-swirl axial vanes 1412 areconfigured to make the inner secondary air in the strong-swirl innersecondary air channel 1411 have a tangential swirling speed.

In an embodiment, the outlet angle θ of the strong-swirl axial vane 1412ranges from 50° to 80°. In other words, the outlet angle θ of thestrong-swirl axial vane 1412 is relatively large, which can make theinner secondary air flowing therethrough have a relatively largetangential swirling speed. Optionally, the strong-swirl axial vane 1412is an axial vane.

In an embodiment, the weak-swirl inner secondary air assembly 142includes a weak-swirl inner secondary air channel 1421 and weak-swirlaxial vanes 1422 disposed in the weak-swirl inner secondary air channel1421. The weak-swirl axial vanes 1422 are configured to make the innersecondary air in the weak-swirl inner secondary air channel 1421 have atangential swirling speed.

In an embodiment, the outlet angle δ of the weak-swirl axial vane 1422ranges from 20° to 50°. In other words, the outlet angle δ of theweak-swirl axial vane 1422 is relatively small, which can make the innersecondary air flowing therethrough have a relatively small tangentialswirling speed. Optionally, the weak-swirl axial vane 1422 is an axialvane.

Optionally, the direct-flow inner secondary air channel 143 is sleevedoutside the weak-swirl inner secondary air channel 1421 throughsupporting ribs 1431. The supporting ribs 1431 are flat in order toavoid producing a tangential swirling speed of the inner secondary air.

The three layers of the strong-swirl inner secondary air assembly 141,the weak-swirl inner secondary air assembly 142, and the direct-flowinner secondary air channel 143 are configured to spray the innersecondary air into the pre-combustion chamber 111. The size of therecirculation zone and the combustion state of the pulverized coal inthe pre-combustion chamber 111 can be flexibly adjusted by adjusting theair volume distribution among the secondary air flows, therebyincreasing the adjustment flexibility of the burner, which is conduciveto the flexible adjustment of the ignition and stable combustion of thepulverized coal under different boiler loads and coal types. Inaddition, the adjustment flexibility of the suppression of NO_(x)production is also increased.

In an embodiment, the reverse jet swirl pulverized coal burner 100further includes an annular connector 160. The annular connector 160 islocated between the strong-swirl inner secondary air assembly 141 andthe primary coal-air structure 120, and connects and fixes thestrong-swirl inner secondary air assembly 141 to the primary coal-airstructure 120. The annular connector 160 can make a certain distancebetween the strong-swirl inner secondary air assembly 141 and theprimary coal-air structure 120 to facilitate the formation of thefirst-stage recirculation zone F in the pre-combustion chamber 111.

Moreover, the direct-flow inner secondary air channel 143 conveys thedirect-flow inner secondary air along the inner wall of thepre-combustion housing 110, which can keep the region adjacent to theinner wall of the pre-combustion housing 110 in an oxidizing atmosphereand prevent unburned coal particles or molten minerals from reaching theinner wall and coking on the wall. In addition, the direct-flow innersecondary air flowing adjacent to the inner wall of the pre-combustionhousing 110 can also cool and protect the pre-combustion housing 110.

In addition, the outer secondary air structure 150 is located outsidethe pre-combustion housing 110, and is configured to transport the outersecondary air. During flowing, the outer secondary air can take away theheat adjacent to the inner wall of the pre-combustion housing 110,thereby further protecting and cooling the pre-combustion housing 110.

In an embodiment, the outer secondary air structure 150 includes anouter secondary air inlet channel 151, an outer secondary air outletchannel 152, and tangential vanes 153. The outer secondary air inletchannel 151 and the outer secondary air outlet channel 152 are connectedand fluid communicated in a stepped manner. The tangential vanes 153 aredisposed in the connection area between the outer secondary air inletchannel 151 and the outer secondary air outlet channel 152. Thetangential vanes 153 are configured to make the outer secondary airflowing therethrough rotate at a high speed. The outer secondary air isintroduced from the outer secondary air inlet channel 151. Under theaction of the tangential vanes 153, the outer secondary air entered theouter secondary air outlet channel 152 can swirl at a high speed and canbe swirly ejected from the outer secondary air outlet channel 152 at thehigh speed. The high-speed swirly ejected outer secondary air helps toform a low-pressure zone at the housing outlet of the pre-combustionhousing 110, thereby forming the third-stage recirculation zone N, whichfurther promotes the burnout and stable combustion of the unburnedpulverized coal ejected from the pre-combustion chamber 111.

By setting three stages of high-temperature fluid recirculation, i.e.,the first-stage recirculation zone F, the second-stage recirculationzone M, and the third-stage recirculation zone N, the coal particles indifferent combustion stages are heated, which is beneficial to ignition,stable combustion, and burnout of pulverized coal under different coaltypes and boiler load conditions.

In an embodiment, the outlet angle y of the tangential vane 153 rangesfrom 15° to 40°.

In an embodiment, the outer secondary air structure 150 further includesa separation annulus 154. The separation annulus 154 is disposed at anend of the outer secondary air outlet channel 152, and located on theouter wall of the expansion section 113. The separation annulus 154 canseparate the flame, sprayed from the pre-combustion chamber 111, fromthe outer secondary air for a distance, thereby delaying the mixingbetween the outer secondary air and the unburned pulverized coalcontained in the flame, and prolonging the combustion time of thepulverized coal in a reducing atmosphere to suppress NO_(x) production.

The working principle of the reverse-jet swirl pulverized coal burner100 with multi-stage recirculations of the present application is asfollows:

The primary coal-air flow is introduced from the primary coal-air flowpipe 121, and flows along a straight line at the initial stage afterentering the primary coal-air flow pipe 121. Under the action of theswirl vanes 123, the primary coal-air flow passing the swirl vanes 123is transformed from a direct flow to a swirling flow. During thehigh-speed swirling of the primary coal-air flow, the coal particles,due to the high density thereof, are subjected to a large centrifugalforce and thrown to the region adjacent to the inner wall of the primarycoal-air flow pipe 121, so that the pulverized coal in the regionadjacent to the inner wall of the primary coal-air flow pipe 121 has ahigher concentration, and the pulverized coal in the central area of theprimary coal-air flow pipe 121 has a lower concentration. With thefurther flowing of the pulverized coal air flow, when the pulverizedcoal air flow reaches the outlet end of the primary coal-air flow pipe121, the air flow with the lower pulverized coal concentration in thecentral area directly faces the fuel-lean coal-air flow pipe 132, sothat this part of the pulverized coal air flow is straightly ejectedfrom the fuel-lean coal-air flow pipe 132, thereby forming the fuel-leancoal-air flow. At the same time, the air flow with the higher pulverizedcoal concentration adjacent to the inner wall of the primary coal-airflow pipe 121 directly faces the recirculation slot 1311 of therecirculation baffle 131. Since the fuel-rich coal-air flow channel 133in a circular shape is formed by the inner wall of the recirculationslot 1311 and the outer wall of the primary coal-air flow pipe 121, thehigh-concentration pulverized coal air flow will enter the fuel-richcoal-air flow channel 133. Guided by the recirculation slot 1311, thehigh-concentration pulverized coal air flow is sprayed into thepre-combustion chamber 111 in the reversed direction along the outerwall of the primary coal-air flow pipe 121, thereby forming thereversely ejected fuel-rich coal-air flow.

In the pre-combustion chamber 111, the inner secondary air is dividedinto three layers, which are respectively introduced from thestrong-swirl inner secondary air assembly 141, the weak-swirl innersecondary air assembly 142, and the direct-flow inner secondary airchannel 143. Wherein, due to the larger outlet angle of the strong-swirlaxial vanes 1412, the inner secondary air entered the strong-swirl innersecondary air channel 1411 produces a larger tangential swirling speedwhen being sprayed into the pre-combustion chamber 111; due to thesmaller outlet angle of the weak-swirl axial vanes 1422, the innersecondary air entered the weak-swirl inner secondary air channel 1421produces a smaller tangential swirling speed when being sprayed into thepre-combustion chamber 111; the inner secondary air entered thedirect-flow inner secondary air channel 143 is not guided by any guidingvanes and is sprayed into the pre-combustion chamber 111 as a directflow. After the overall inner secondary air is sprayed into thepre-combustion chamber 111 as above, a speed distribution is formed suchthat the swirling strength of the inner secondary air is graduallyreduced to zero from the inner side to the outer side in thepre-combustion chamber 111.

Since the inner secondary air adjacent to the primary coal-air flow pipe121 has a relatively large swirling tangential speed, during thehigh-speed swirling of the air flow, a low pressure zone is formed inthe central area of the swirling flow. In addition, since the inner wallof the pre-combustion housing 110 has an inclination angle, during theflowing of the inner secondary air from top to bottom in thepre-combustion chamber 111, the flow area of the air flow graduallyexpands, so that the flow rate of the air flow decreases, and the staticpressure gradually increases. The above two reasons work together tomake part of the inner secondary air flow reversely to the low pressurezone during the flowing of the inner secondary air in the pre-combustionchamber 111, thus forming the first-stage recirculation zone F.

Since the fuel-rich coal-air flow is injected to the place adjacent tothe first-stage recirculation zone F, the fuel-rich coal-air flow can beeasily entrained into the first-stage recirculation zone F during theflowing. The fuel-rich coal-air flow whirls, burns, and releases heat inthe first-stage recirculation zone F, and then passes by therecirculation baffle 131 and ejects out from the pre-combustion chamber111.

When the high-temperature flow passes by the conical recirculationbaffle 131, a low-pressure zone can be formed behind the recirculationbaffle 131, so that part of the high-temperature fluid will recirculatebehind the recirculation baffle 131 to form a second-stage recirculationzone M. This part of the recirculated high-temperature fluid meets thefuel-lean coal-air flow ejected from the recirculation baffle 131, whichwill promote the temperature increasing of the fuel-lean coal-air flow,heating and igniting the fuel-lean coal-air flow. Then, the air flowsand unburned pulverized coal particles in the pre-combustion chamber 111are ejected out from the pre-combustion chamber 111. At this time, theouter secondary air is introduced from the outer secondary air inletchannel 151. Passing by the tangential vanes 153, the outer secondaryair entered the outer secondary air outlet channel 152 swirls at a highspeed and swirly ejected from the outer secondary air outlet channel 152at the high speed. The high-speed swirly ejected outer secondary airhelps to form the third-stage recirculation zone N at the housing outletof the pre-combustion housing 110, thereby forming the high temperaturerecirculation fluid at the outlet of the pre-combustion chamber 111,which further promotes the burnout and stable combustion of the unburnedpulverized coal ejected from the pre-combustion chamber 111.

The technical features of the above-mentioned embodiments can becombined arbitrarily. In order to make the description concise, not allpossible combinations of the technical features are described in theembodiments. However, as long as there is no contradiction in thecombination of these technical features, the combinations should beconsidered as in the scope of the present application.

The above-described embodiments are only several implementations of thepresent application, and the descriptions are relatively specific anddetailed, but they should not be construed as limiting the scope of thepresent application. It should be understood by those of ordinary skillin the art that various modifications and improvements can be madewithout departing from the concept of the present application, and allfall within the protection scope of the present application. Therefore,the patent protection of the present application shall be defined by theappended claims.

What is claimed is:
 1. A reverse-jet swirl pulverized coal burner withmulti-stage recirculations, comprising: a pre-combustion housing, thepre-combustion housing having a pre-combustion chamber and a housingoutlet located on one side of the pre-combustion chamber; a primarycoal-air structure passing through the pre-combustion housing andextending into the pre-combustion chamber, the primary coal-airstructure being configured to separate a primary coal-air flow into afuel-rich coal-air flow and a fuel-lean coal-air flow, and an outlet endof the primary coal-air structure extending toward the housing outlet; arich-lean output structure disposed at the outlet end of the primarycoal-air structure, the rich-lean output structure being configured tooutput the fuel-lean coal-air flow and block the fuel-rich coal-air flowto make the fuel-rich coal-air flow reversely flow to the pre-combustionchamber; an inner secondary air structure disposed on the pre-combustionhousing and around the primary coal-air structure, the inner secondaryair structure is configured to introduce an inner secondary air into thepre-combustion chamber, thereby forming a first-stage recirculation zonein the pre-combustion chamber and forming a second-stage recirculationzone at an end of the rich-lean output structure away from the primarycoal-air structure; and an outer secondary air structure sleeved outsidethe pre-combustion housing, the outer secondary air structure beingconfigured to transport an outer secondary air, thereby forming athird-stage recirculation zone at the housing outlet.
 2. The reverse-jetswirl pulverized coal burner with multi-stage recirculations of claim 1,wherein the pre-combustion housing comprises a cone section and anexpansion section connected to the cone section, an end of the expansionsection away from the cone section is the housing outlet of thepre-combustion housing; an inclination angle of the expansion section isgreater than an inclination angle of the cone section.
 3. Thereverse-jet swirl pulverized coal burner with multi-stage recirculationsof claim 1, wherein the inclination angle a of the cone sectionsatisfies 0°<α≤20°, and the inclination angle β of the expansion sectionis in a range from 20° to 50°.
 4. The reverse-jet swirl pulverized coalburner with multi-stage recirculations of claim 1, wherein the primarycoal-air structure comprises a primary coal-air flow pipe, a fixingaxle, and a plurality of swirl vanes; the fixing axle is locatedadjacent to an outlet end of the primary coal-air flow pipe; theplurality of swirl vanes are connected to an inner wall of the primarycoal-air flow pipe and the fixing axle, and are configured to separatethe primary coal-air flow into the fuel-rich coal-air flow and thefuel-lean coal-air flow.
 5. The reverse-jet swirl pulverized coal burnerwith multi-stage recirculations of claim 4, wherein the rich-lean outputstructure comprises a recirculation baffle and a fuel-lean coal-air flowpipe penetrating through the recirculation baffle; the recirculationbaffle is located at the outlet end of the primary coal-air flow pipe; asurface of the recirculation baffle facing the primary coal-air flowpipe has a recirculation slot; the recirculation slot is configured toguide the fuel-rich coal-air flow to flow reversely to thepre-combustion chamber; a shape of an inner wall of the recirculationslot is straight or curved; a fuel-rich coal-air flow channel with acircular cross-section is formed between the inner wall of therecirculation slot and an outer wall of the primary coal-air flow pipeto reverse the fuel-rich coal-air flow; the fuel-lean coal-air flowpipe, having one end extending into a central area of the outlet end ofthe primary coal-air flow pipe, is configured to output the fuel-leancoal-air flow coming from the primary coal-air flow pipe.
 6. Thereverse-jet swirl pulverized coal burner with multi-stage recirculationsof claim 5, wherein the recirculation baffle has a conical shape, and across-sectional size of an end of the recirculation baffle toward theprimary coal-air flow pipe is smaller than a cross-sectional size ofanother end of the recirculation baffle away from the primary coal-airflow pipe; the rich-lean output structure comprises a fixing rib thatconnects the recirculation baffle to the primary coal-air flow pipe. 7.The reverse-jet swirl pulverized coal burner with multi-stagerecirculations of claim 1, wherein the inner secondary air structurecomprises a strong-swirl inner secondary air assembly, a weak-swirlinner secondary air assembly, and a direct-flow inner secondary airchannel; the strong-swirl inner secondary air assembly is sleevedoutside the primary coal-air structure, the weak-swirl inner secondaryair assembly is sleeved outside the strong-swirl inner secondary airassembly, the direct-flow inner secondary air channel is sleeved outsidethe weak-swirl inner secondary air assembly; tangential swirling speedsof the secondary air respectively conveyed by the strong-swirl innersecondary air assembly, the weak-swirl inner secondary air assembly, andthe direct-flow inner secondary air channel gradually decrease.
 8. Thereverse-jet swirl pulverized coal burner with multi-stage recirculationsof claim 7, wherein the strong-swirl inner secondary air assemblycomprises a strong-swirl inner secondary air channel and strong-swirlaxial vanes disposed in the strong-swirl inner secondary air channel;the strong-swirl axial vanes are configured to make the inner secondaryair in the strong-swirl inner secondary air channel have a tangentialswirling speed; an outlet angle θ of the strong-swirl axial vanes rangesfrom 50° to 80°.
 9. The reverse-jet swirl pulverized coal burner withmulti-stage recirculations of claim 7, wherein the weak-swirl innersecondary air assembly comprises a weak-swirl inner secondary airchannel and weak-swirl axial vanes disposed in the weak-swirl innersecondary air channel; the weak-swirl axial vanes are configured to makethe inner secondary air in the weak-swirl inner secondary air channelhave a tangential swirling speed; an outlet angle δ of the weak-swirlaxial vanes ranges from 20° to 50°.
 10. The reverse-jet swirl pulverizedcoal burner with multi-stage recirculations of claim 7, wherein themulti-stage recirculation reverse-jet swirl pulverized coal burnerfurther comprises an annular connector; the annular connector is locatedbetween the strong-swirl inner secondary air assembly and the primarycoal-air structure, and connects and fixes the strong-swirl innersecondary air assembly to the primary coal-air structure.
 11. Thereverse-jet swirl pulverized coal burner with multi-stage recirculationsof claim 2, wherein the outer secondary air structure comprises an outersecondary air inlet channel, an outer secondary air outlet channel, andtangential vanes; the outer secondary air inlet channel and the outersecondary air outlet channel are connected and fluid communicated in astepped manner; the tangential vanes are disposed in a connection areabetween the outer secondary air inlet channel and the outer secondaryair outlet channel.
 12. The reverse-jet swirl pulverized coal burnerwith multi-stage recirculations of claim 11, wherein an outlet angle yof the tangential vane ranges from 15° to 40°.
 13. The reverse-jet swirlpulverized coal burner with multi-stage recirculations of claim 11,wherein the outer secondary air structure further comprises a separationannulus; the separation annulus is disposed at an end of the outersecondary air outlet channel, and located on an outer wall of theexpansion section.